In mixer systems, fluids to be mixed may be separately divided into a plurality of fluid flow filaments, which all together pass through feeders and flow into mixing chambers via inlets. The so-achieved closely adjacent relationship between individual micro-flow filaments of the two or more fluid fractions enables effective mixing to be obtained over a short distance and in a very short time.
German Patent DE 44 16 343 C2 describes an example of a mixer including a mixing chamber and an upstream guide structure for separately feeding fluids to be mixed to a mixing chamber. The guide structure has dimensions in the millimeter range and is formed by a plurality of stacked foils which each have a thickness of about 100 μm and in which the channels are formed as microstructures. The channels of a foil include feeders for only one of the two fluid fractions. In one embodiment, the mixing chamber opens directly into the microchannels of a downstream heat exchanger or microreactor.
A similar mixer, in which the feed channels for two fluids to be mixed or dispersed extend in curved paths and discharge in parallel into the mixing chamber, but which is otherwise of the same construction and operating principle, is described in DE 195 40 292 C1. This arrangement is expected to allow mixing to occur with the same efficiency and speed over the whole discharge cross-sectional area within the mixing chamber. The guide channels have substantially constant cross sections and widths smaller than 250 μm. The foils into which the channel structures are formed have a thickness of about 100 μm.
German Patent Application DE 101 23 093 A1 also describes a static micromixer for mixing at least two fluids, including a plurality of structured foils stacked on top of one another. However, the mixing chamber is formed by a circular opening in a foil; the inlets of the two fluids being formed on the same foil in such a manner that they are arranged in alternating sequence in one plane over the cylindrical wall of the mixing chamber and over the entire height thereof. During mixing, a two-dimensional helical flow is created in the mixing chamber. This helical flow discharges through a hole provided in one end face of the mixing chamber concentrically with the axis of symmetry thereof, said end face being formed by a foil surface bounding the mixing chamber.
International Patent Application WO 02/089966 A2 A also describes a similar mixing apparatus for mixing at least two fluids, in which the flow is directed along a helical path. However, in that patent, the fluids are additionally mixed in mixers in the feed lines before they enter the mixing chamber.
However, when a flow is directed along a helical path in the manner mentioned above, the flow is constricted as a natural consequence. This flow constriction creates an appreciable resistance to flow, which significantly limits the potential throughput or results in an increasing velocity of flow.
U.S. Pat. No. 5,573,334 also describes a static mixer for two fluid fractions, including a cylindrical mixing chamber having two end portions. One inlet for each fluid fraction and a common outlet are positioned in one of the end portions, respectively. Here too, the outlet is provided in the form of a concentric hole in the bottom of the cylindrical mixing chamber, which always involves the aforementioned effects.
A particularly large mixing contact area between the fluids to be mixed is achieved through miniaturization by dividing the fluids into micro-flow filaments. Thus, mixing does indeed occur rapidly and completely, but at a relatively low fluid throughput. On the other hand, any increase in the dimensions would, in fact, increase the potential fluid throughput, but would be associated with a decrease in the specific mixing contact area between the fluids to be mixed. Practical tests have shown that in the aforementioned mixers, a simple increase in entry channels to a mixing chamber involves the risk that unavoidable manufacturing inaccuracies, plugging, and inhomogeneities of flow in the individual fluid feed channels may result in inhomogeneous introduction of the fluid fractions to be mixed into the mixing chamber.
If a mixer system of the type mentioned above is to be used to produce a reactive fluid mixture which, after mixing, is to be introduced into a reactor volume for subsequent chemical reaction, instantaneous and yet homogeneous mixing is of particular importance. To this end, it is important that the homogeneous mixture be transferred into the reaction volume for subsequent, controlled chemical reaction in a very short time, namely before backmixing may occur, or before a premature start of the reaction.